Photonic integration has been driven by the ever growing demand for smaller size, lower cost, lower power consumption, easier assembly, higher reliability, and greater data density in modern photonic devices and systems. Among the many platforms, silicon photonics is particularly promising for photonic integration due to the leveraging of existing electronic integrated circuit facilities for large-scale manufacturing [1]. Monolithic integration in silicon is challenging, however, due to the limited active properties of silicon, thereby creating a need for hybrid integration [2]. Materials integrated on silicon include semiconductors, polymers, ferroelectric oxides, metal oxides, graphene and so on [2-7]. A variety of hybrid integrated photonic devices have been demonstrated on the silicon platform including lasers, detectors, modulators, amplifiers, tunable filters, and polarization rotators [8-11].
The lack of a second order susceptibility in unstrained silicon is one of the drivers for hybrid integration [12]. Recently, a hybrid silicon and LiNbO3 material system has been introduced by bonding ion-sliced LiNbO3 to silicon waveguides, enabling compact sensors, filters, and modulators on silicon based on the second order susceptibility of LiNbO3 [13-18]. Hybrid Si/LiNbO3 modulators have the potential to advance the state of the art with respect to speed, linearity, chirp, insertion loss, and power consumption [16, 19]. More broadly, Si/LiNbO3 devices with advanced functionalities are envisioned that exploit the well-understood electro-optical, piezoelectric, and nonlinear optical properties of LiNbO3 [20, 21].
For hybrid integration, ion-sliced LiNbO3 platelets have been produced by ion implantation on LiNbO3 wafers followed by either wet etching or thermal blistering treatment [13-17, 22]. During wet etching, lateral etching of the damage layer introduced by ion implantation results in the exfoliation of LiNbO3 platelets from the bulk wafer. The etching rate depends on the crystal orientation and is as low as 100 nm min−1 for x-cut LiNbO3 [23]. Furthermore, the achievable platelet area decreases as the thickness decreases. For thermal treatment, the wafer surface blisters into random platelets due to thermal stress. While submicrometer thick LiNbO3 with edge lengths in the range of tens of microns to hundreds of microns can be obtained, the resulting random platelets exhibit uncontrolled size, shape, and unknown orientation of the crystal axes. For example, LiNbO3 platelets having various widths of about 15-100 micrometers and various lengths of about 0.1-2 mm with unknown crystal orientation can result. The lack of control of the ion-sliced LiNbO3 limits the fabrication yield, device size, and design flexibility of Si/LiNbO3 devices. Particularly, electro-optic devices with electric fields applied along the z-axis for efficient modulation cannot be realized using a random platelet with unknown z-axis.